1. Field of the Invention
The present invention relates to a method and apparatus for a linear operated type metal forming process for obtaining, efficiently and precisely, a deep recessed pattern on a partial or an entire surface of a tubular blank material having an axial hollow space of a desired cross sectional shape such as triangle, a square, a polygonal, an odd or a circular shape. The present invention can, for example, be preferably utilized for obtaining a so-called VGR type rack bar as a part in a steering device of an automobile. However, the present invention can also be utilized in any different field of application for obtaining a mechanical part or an ornamental product where a formation of a projected or recessed pattern on its surface is required.
2. Description of Related Art
In Japanese Examined Patent Publication (kokoku) No. 3-5892, a metal forming technique for producing, from a hollowed member (a pipe), a rack bar as a part in a steering device is disclosed. In a metal forming process of a rack bar in this patent, a pipe member, which is thermally softened, is held in a die and is subjected to a pressing so that the pipe member is flattened at a location where a rack is to be formed. Then, a die having straight teeth is engaged with the flattened part of the pipe member, while a mandrel is inserted to the central bore of the pipe member. The mandrel is provided with a tapered operating portion, which is engaged with an inner surface of the flattened portion and is forced into the axial bore of the pipe member, which causes the material to be radially outwardly flown into the cavities of the die, thereby forming, on the flattened portion of the pipe member, the straight teeth of which correspond to the straight teeth on the formation die.
The Japanese ""892 patent is directed to a formation of a rack bar by a forced penetration of the mandrel into the pipe under an outwardly heated condition. Namely, when the pipe is subjected to a flattening process, the pipe is, at the portion to be flattened, subjected to a heating process, which causes the flattened portion to be softened. Such a softening of the flattened portion causes the later to be inwardly and centrally thickened, thereby causing the flattened portion to be shaped as a convex lens at a transverse cross section thereof. Due to such cross sectional shape of the convex lens of the flattened portion of the pipe, the degree of the engagement of the mandrel with the flattened portion of the pipe can be increased.
The technique disclosed by the Japanese ""892 patent is defective in terms of a reduced precision of products, which makes it difficult that the products are actually used. Furthermore, the prior art method is defective also in that its production cost is high due to the fact that the process is complicated, on one hand and that, on the other hand, the cost of the device is high.
In view of the above, an object of the present invention is to provide a technique for metal forming capable of overcoming the above-noted difficulties in the prior art.
Another object of the present invention is to provide a technique for a metal forming capable of obtaining an increased precision, while preventing the process from being complicated.
According to the first aspect of the present invention, a process is provided for producing an article with toothed portions, such as a pipe shaped rack bar, comprising the steps of:
a) providing a die having, at its inner surface, toothed portions;
b) holding a blank pipe in the die;
c) providing a mandrel having a tapered operating head;
d) inserting, repeatedly, the mandrel into an axial space of the blank pipe, so that the operating head of the mandrel causes the material to flow radially outwardly toward the inner surface of the die, thereby generating toothed portions on the blank pipe corresponding to the toothed portions of the die;
e) keeping, during the repeated insertions of the mandrel, an increased temperature of the work generated by a heat substantially solely by the execution of the insertion of the mandrel to the blank pipe, which temperature is substantially in a range where a so-called work-softening phenomenon is obtained;
f) preventing, during the repeated insertions of the mandrel, the metal from being subjected to an age-hardening, and;
g) maintaining an increased temperature of the work generated substantially solely by a heat due to the execution of the insertion of the mandrel to the blank pipe.
According to this aspect of the invention, during the execution of the metal forming by the repeated insertion of the mandrel to the blank pipe, quasi-warm or semi-warm working condition of a temperature around 200xc2x0 C. substantially solely generated by the metal is maintained, while preventing an age-hardening from being occurred, resulting in an increased degree of a flowability of metal. Furthermore, under such an increased degree of the flowability of metal, a cancellation of any deviated flow of metal to the die is done, thereby producing a rack bar having teeth of a precision as fine as 32 xcexcm. Furthermore, according to the present invention, an introduction a blank pipe to the die-set is done under a room temperature, and any pre-heating process is unnecessary. Furthermore, once a clamping of a blank pipe by the die set is done, all the processes for the metal forming of the rack bar are completed without opening the die set. Thus, a highly increased production efficiency is obtained, resulting in a reduced production cost.
According to a second aspect of the invention, a process is provided for producing a rack bar, comprising the steps of:
a) providing a die having, at its inner surface, toothed portions along the length of the die;
b) holding a blank pipe in the die;
c) providing mandrels each having at least one tapered operating head;
d) inserting, repeatedly, the mandrels into an axial space of the blank pipe so that the operating head of the mandrel causes the material to be flown radially outwardly toward the inner surface of the die, thereby generating toothed portions on the blank pipe corresponding to the toothed portions of the die;
e) reversing, alternately, the direction of the insertion of mandrels to the blank pipe for keeping a symmetrical flow of a metal toward the die, and;
f) overlapping the insertion of the mandrel one side of the blank pipe and the withdrawal of the mandrel on the other side of the blank pipe, such that the insertion of the mandrel to the blank pipe in one direction is commenced prior to the completion of withdrawal of the mandrel from the blank pipe in the other direction, and;
g) maintaining an increased temperature of the work generated substantially solely by a heat due to the execution of the insertion of the mandrel to the blank pipe.
According to this aspect, a rack bar of an increased precision can be obtained irrespective of a fact that the production is done under a metal forming principle. Thus, the production efficiency as well as a cost can be highly reduced.
According to the third aspect of the present invention, a pipe shaped rack bar is provided, which is made, purely, of metal forming process from a blank pipe, wherein said metal forming process is such that the blank pipe is subjected to repeated insertions of a mandrel alternately between opposite sides of the blank pipe, while keeping a semi-warm working condition of a temperature around 200xc2x0 C. substantially solely generated by the execution of the metal forming process, while preventing an age-hardening from being generated, while preventing an occurrence of a deviated flow of metal to the die.
According to this, aspect of the present invention, the rack bar is purely made by a metal forming process. In other words, while any machining process is substantially unnecessary, a precision as fine as 32 micron can be obtained.
According to a fourth aspect of the invention, a pipe shaped rack bar is provided, which is made, purely, of metal forming process from a blank pipe by inserting a mandrel to the hollow space in the blank pipe held by a die having toothed portions, wherein said rack bar having toothed portion corresponding to the toothed portions of the die and wherein each of the teeth in the toothed portion of the rack bar has layers which are symmetrical to the center of the teeth.
According to this aspect of the invention, the rack bar has, at its toothed portion, symmetrical flown layers, which can prevent any non-uniform spring back amount, which otherwise causes the precision of the rack bar to be worsened.
According to a fifth aspect of the present invention, a mandrel is provided for use together with a die having, at its inner surface, toothed portions for effecting a metal forming process, wherein the mandrel is inserted to a blank pipe held by the die so that a radially outward metal flow under the plastic deformation is obtained, thereby forming, on the blank pipe, teeth corresponding to the toothed portions of the die, said mandrel comprising axially spaced heads having respective operating diameters, the values of the operating diameters being increased in the direction of an increase in the insertion depth of the mandrel.
According to this aspect of the invention, the provision of the axially spaced heads allows a multistage expansion of the material to be obtained during a single insertion of the mandrel, thereby increasing an efficiency in the metal forming process.
According to a sixth aspect of the invention, a die assembly is provided, comprising a die holder having an outwardly opened and longitudinally extending recess, a toothed die detachably housed in said recess and at least one tapered piece press fitted to said recess of the die holder for causing the toothed die to be longitudinally urged, so that the toothed die is fixedly held in the recess of the die holder, said die holder having a hole extending therethrough and opened to said tapered piece at a bottom surface of the recess, the hole being for receiving a presser which is engaged with the pin for causing the tapered piece to be withdrawn from said recess, thereby allowing the die assembly to be dismantled.
According to this aspect of the invention, the use of tapered pieces allows the assembly to be firmly assembled, thereby preventing any rattling, thus resulting in an increased service life. Furthermore, any additional press fitting as well as shrinkage fitting are unnecessary, resulting in a reduced production cost.
According to a seventh aspect of the present invention, a linearly operated metal forming device is provided for producing a pipe shaped rack bar from a blank pipe, said device comprising:
a plurality of die sets, each die set being capable of moved between a closed position for holding a blank pipe as a work and an opened position for allowing the work to be taken out;
a bed on which said die sets are arranged in parallel;
a first presser of said die sets, by which the die sets are laterally adjoined with each other while the blank pipes are held by the respective die sets;
mandrels to be inserted to the respective blank pipes;
a mandrel holder for holding, in parallel, the mandrels at a predetermined spacing, and;
a second presser of said mandrel holder, by which the mandrels held by the holder are simultaneously inserted to the respective blank pipes held by the respective die sets, so that the blank pipes are subjected simultaneously to the metal forming process, thereby forming, on the outer surfaces of the blank pipes, teeth corresponding the toothed portions of the respective die sets.
According to this aspect of the invention, during the execution of metal forming process of the rack bars, the die sets are arranged on the bed under a laterally adjoined relationship. As a result, the toppling moment as generated by the insertion of mandrels to the respective die sets are cancelled between the die sets, which are adjoined with each other. This arrangement is advantageous in that a single usage of the cylinder (presser) is sufficient for closing the die sets irrespective of the number of the die sets on the bed. Furthermore, since the cancellation of the toppling moment between the adjacent die sets, an output of the cylinder for keeping the die sets to be closed is unchanged, which is advantageous in that a reduced size of the cylinder can be used.
According to an eighth aspect of the invention, a linear operated metal forming device is provided for producing a pipe shaped rack bar from a blank pipe, said device comprising:
a plurality of die sets, each die set being capable of moved between a closed position for holding a blank pipe as a work and an opened position for allowing the work to be taken out;
a bed on which said die sets are arranged in parallel;
a first presser of said die sets, by which said die sets are laterally adjoined with each other while the blank pipes are held by the respective die sets;
mandrels to be inserted to the respective blank pipes;
a plurality of mandrel holders, each of which is for holding, in parallel, the mandrels at a predetermined spacing;
a stacker for holding mandrels so that they are stacked with each other;
the arrangement of the mandrels between the stacked holders being such that the degree of the metal forming is progressed in the stacked direction;
a second presser by which the stacker are progressively shifted in the stacker so that the mandrel holders of different stages are progressively aligned with the die sets, and;
a third presser by which the mandrels held by the aligned mandrel holder are simultaneously inserted to the respective blank pipes in the die sets and withdrawn from the respective blank pipes, thereby executing a multi-stage working by progressively changing the mandrels inserted to the blank pipes by the stepwise displacement of the mandrel holders in the stacker.
According to this aspect of the invention, the mandrel holders for holding mandrels are capable of being shifted in the stacker in accordance with the progress of the operating steps of the rack bars. Thus, a multi-stage working of the blank pipes by a simultaneous insertion of the mandrels is done while progressively changing the operating diameters of the mandrels by shifting the mandrel holders in the stacker. Thus, the efficiency in the rack bar production can be highly increased.
According to nineth aspect of the invention, a linear operated metal forming device is provided for producing a pipe shaped rack bar from a blank pipe, comprising:
a plurality of die sets, each die set being capable of moved between a closed position for holding a blank pipe as a work and an opened position for allowing the work to be taken out;
a bed on which said die sets are arranged in parallel;
a first presser of said die sets, by which said die sets are laterally adjoined with each other while the blank pipes are held by the respective die sets;
mandrels to be inserted to the respective blank pipes;
a plurality of mandrel holders, each of which is for holding, in parallel, the mandrels at a predetermined spacing;
a pair of stackers for holding mandrels so that they are stacked with each other, one of the stackers being arranged on one side of the bed while the other stacker is arranged on the opposite side of the bed;
the arrangement of the mandrels between the stacked mandrel holders being such that the degree of the metal forming is progressed in the stacked direction;
a second presser by which the mandrel holders on one of the stackers are progressively shifted in the stacker so that the mandrel holders are progressively aligned with the die sets;
a third presser by which the mandrel holders on the other stackers are progressively shifted in the stacker so that the mandrel holders are progressively aligned with the die sets;
a fourth presser by which the mandrels held by the aligned mandrel holder in one of the stackers are simultaneously inserted to the respective blank pipes in the die sets and withdrawn from the respective blank pipes, and;
a fifth presser by which the mandrels held by the aligned mandrel holder in the other stacker are simultaneously inserted to the respective blank pipes in the die sets and withdrawn from the respective blank pipes;
the arrangement being such that, at each shifted position of the stackers, an alternated insertion to the blank pipes is done between the mandrels held by the mandrel holders aligned with the die sets in one of the stackers and the mandrels held by the mandrel holders aligned with the die sets in the other stackers.
According to this aspect of the invention, the insertion of the mandrels held by the mandrel holders at an operating stage is done alternately between the left-hand and right-hand stackers. Thus, increased precision of the rack bars is obtained while keeping increased production efficiency.
According to a tenth aspect of the invention, a linear operated metal forming device is provided for producing a pipe shaped rack bar from a blank pipe, comprising:
a die set for holding a blank pipe, said die set having toothed portions faced with the blank pipe;
a bed on which said die set is arranged;
a mandrel to be inserted to the blank pipe held by the die set, so that teeth corresponding to the toothed portions on the die are formed on the blank pipe;
a hydraulic cylinder for causing the mandrel to be reciprocated;
a first rib extending, in a cantilever fashion, from the bed, and;
a second rib extending, in a cantilever fashion from a free end of the first rib, said second rib having a free end fixedly connected to the hydraulic cylinder;
the arrangement of the first and second ribs being such that, during the metal forming by the insertion of the mandrel to the blank pipe, the deflection of the first rib and the deflection of the second rib are opposite each other so that they are substantially crossed out, thereby keeping an alignment of the axis of the cylinder with the axis of the blank pipe.
According to this aspect of the invention, any deflection of the axial of the mandrels is cancelled irrespective of a cantilever nature of the machine frame. Thus, an increased service like is obtained, while keeping an increased production efficiency.